From the globular to the fibrous state: protein structure and structural conversion in amyloid formation
The term ‘amyloid’ was used originally to describe certain deposits found post- mortem in organs and tissues, which gave a positive reaction when stained with iodine (Virchow, 1854). Only later was it realized that the material was in fact predominantly proteinaceous, although it is known to be associated with carbohydrates, particularly glucosoaminoglycans, when obtained from many ex vivo sources. With the increasing precision in the definition of amyloid, initially from its characteristic green birefringence when stained with the dye Congo Red (Missmahl & Hartwig, 1953), and later from its particular appearance under the electron microscope (Cohen & Calkins, 1959) and its X-ray diffraction pattern (Eanes & Glenner, 1968), it has become evident that it is a specific fibrillar protein state, which can also be formed by some proteins when denatured in vitro (Burke & Rougvie, 1972), and by synthetic oligopeptides (Bradbury et al. 1960) that may form amyloid spontaneously when placed in pure aqueous medium (Serpell, 1996). Although these latter may form useful experimental systems for the study of amyloid, its major interest at present is that it is associated with a number of prominent lethal diseases (Benson & Wallace, 1989; Pepys, 1994).
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